1. Field of the Invention
This invention relates to a laminate type dielectric device such as a laminate-type capacitor, a laminate-type piezoelectric actuator, etc, a production method, and an electrode paste material for forming an electrode layer of the dielectric device.
2. Description of the Related Art
A laminate-type dielectric device produced by alternately laminating dielectric ceramic layers having various dielectric properties and electrode layers have been widely used in the past. Known electrode materials for forming these electrode layers include Pt, Pd, Ag, Ni, Cu, their mixtures and their alloys.
The problems encountered in producing the electrodes vary from electrode material to electrode material. Silver (Ag), for example, has a high dielectric constant and is relatively economical. However, Ag has a low melting point of 980xc2x0 C. and is likely to invite migration and, therefore, has low reliability.
In contrast, palladium (Pd) is expensive but has a high melting point. Pd has therefore been used in the form of an Agxe2x80x94Pd metal material to suppress migration and to raise the melting point of the electrode material (refer to Japanese Unexamined Patent Publication (Kokai) No. 5-304043).
The addition of Pd can suppress migration, it is true, but bonding is not sufficient between the electrode material and a ceramic material. Various measures have been taken to cope with this problem as described in Japanese Unexamined Patent Publications (Kokai) Nos. 5-304043 and 8-255509.
Nickel (Ni) involves the problems such as the occurrence of cracking and deformation and so-called xe2x80x9cislandingxe2x80x9d of the electrode due to superheating (rapid sintering of Ni at a temperature exceeding 1,000xc2x0 C.). To cope with the problems, Japanese Unexamined Patent Publication (Kokai) No. 5-55077 proposes to mix Ni and NiO, and Japanese Unexamined Patent Publication (Kokai) No. 6-290985 proposes to add an oxide of a rare earth element.
Among them, the prior art technology using Ag aims at solving the problem that results from Ag, and the prior art technology using Ni aims at solving the problem of the superheating of Ni that is peculiar to Ni. However, these materials are expensive and, as long as these materials are used, it will be difficult to reduce the production cost of the laminate type dielectric device that has been widely used.
On the other hand, copper (Cu) could be a promising material among base metals as the economical electrode material. In connection with Cu-containing paste materials or electrodes, a technology is known that suppresses the occurrence of cracking resulting from oxidation expansion of Cu by mixing Cu and C2O in a suitable proportion (Japanese Unexamined Patent Publication (Kokai) No. 5-283274). Further, there are also known a method that forms a complex by using an organic phosphorus compound a metal (Cu) ion, and baking the complex to assist sintering of ceramics and to make the film thickness uniform (Japanese Unexamined Patent Publication (Kokai) No. 5-242724), and a method that suppresses the occurrence of warping and cracking of the device by limiting the Cu content to 40 to 70 wt % to reduce the coating thickness (Japanese Unexamined Patent Publication (Kokai) No. 5-234414).
Still another known technology uses a paste material containing 40 to 60 wt % of Cu powder having a mean particle diameter of 0.5 to 2 xcexcm and a particle size distribution of 0.3 to 4 xcexcm where the paste material is baked to a film thickness of 1 to 3 xcexcm so as to (1) suppress the occurrence of voids between the device and the electrode and inside the electrode, (2) suppress the occurrence of breakage of the electrode resulting from warp of inner and outer electrodes, (3) prevent deformation of a ceramic component itself and (4) prevent inferior contact between the inner electrode and the outer electrode (Japanese Unexamined Patent Publication (Kokai) No. 5-190375). The methods and objects of using Cu electrodes are very diversified.
One of the prior art references that relates to the improvement of oxidation resistance of the Cu type electrode materials is Japanese Unexamined Patent Publication (Kokai) No. 7-230714. The technology described in this reference suppresses the oxidation of copper powder on the basis of the principle that, when a metallic boride is blended, boron is oxidized in preference to copper powder.
In contrast, the present invention that will be explained later does not prevent oxidation of the Cu electrode portion.
In order to obtain a laminate product between ceramic materials, particularly PZT type materials that will generically have a Pb(Zr, Ti)O3 type perovskite structure while a boundary portion remains under a satisfactory condition, it is preferred to simultaneously bake the laminate of the PZT type material and the Cu electrode material. However, the PZT type material is preferably baked in the oxidizing atmosphere because it is an oxide whereas the Cu electrode material is preferably baked in the reducing atmosphere, for example, because the Cu electrode material needs a high conductivity.
Adjustment of the baking atmosphere that simultaneously satisfies the requirements for the PZT type material and the Cu electrode material is not impossible. Even when such an adjustment of the atmosphere is realized, however, the problem yet remains unsolved as to whether or not the atmosphere condition can sufficiently exploit performance of the laminate product. For example, when the atmosphere condition is such that the Cu electrode material can be sufficiently reduced, the PZT type material is presumably reduced to a certain extent, too. Needless to say, the performance of PZT drops if the PZT type material is reduced.
The condition that permits sufficient reduction of the Cu electrode material may well be the condition that permits also PZT to sufficiently exhibit its performance. If the drop of performance is restricted for the secondary factor that bonding can be sufficiently maintained, for example, a drop of in performance results from partial reduction.
In other words, according to the prior art technologies, reduction partially deteriorates the piezoelectric property, partial contraction (expansion) invites the occurrence of de-lamination and curving and a drastic drop in performance. In contrast, according to the present invention, the demerit is only the drop of performance by partial reduction.
Performance of PZT may be improved by gradually weakening the reducing condition during the process, though the Cu material is sufficiently reduced once, so as to mitigate the degree of reduction of PZT.
In view of the problems of the prior art described above, the present invention is directed to provide a laminate type dielectric device capable of sufficiently bonding an electrode material, such as Cu, to a ceramic material by using an economical base metal material such as Cu, and fully exploiting the characteristics of a dielectric ceramic layer, a production method thereof, and an electrode paste material.
According to a first aspect of the present invention, there is provided a laminate type dielectric device formed by alternately laminating dielectric ceramic layers and electrode layers, wherein the electrode layers are mainly made of an electrically conductive base metal material having greater standard Gibbs free energy of the formation of metal oxides at a baking temperature than that of ceramic materials constituting the dielectric ceramic layers, and segregation of materials inclusive of the electrically conductive base metal material does not occur at a portion sandwiched between adjacent positive and negative electrode layers in the dielectric ceramic layers.
The term xe2x80x9cportion sandwiched between the adjacent positive and negative electrode layers in the dielectric ceramic layersxe2x80x9d represents the region that is sandwiched between the overlapping portion when the positive electrode layer and the negative electrode layer are seen in the laminating direction. When the positive or negative electrode layer has a portion that does not operate as the electrode due to its discontinuity, a portion of the dielectric portion opposing the former portion does not correspond to the portion sandwiched between the electrode layers described below.
The term xe2x80x9csegregationxe2x80x9d of the material inclusive of the electrically conductive base metal material described above represents the condition in which the electrically conductive base metal having intensity of at least 60% is not detected inside the dielectric ceramic layers with respect to the intensity of the electrically conductive base metal in the electrode layers when component analysis is conducted for the electrode layers and the dielectric ceramic layers by EPMA, respectively. The substance detected in this case is not particularly limited to the metal (inclusive of the case where the substance is detected as the component element). The term xe2x80x9cintensityxe2x80x9d represents the detection intensity by an electronic probe micro-analyzer (EPMA), and the term xe2x80x9cintensity of at least 60%xe2x80x9d may correspond well to an intensity ratio under the following apparatus condition:
Next, the function and effect of the present invention will be explained.
In the laminate type dielectric device according to the present invention, the electrode layers are made of an electrically conductive base metal material having a greater standard Gibbs free energy for forming a metal oxide at a baking temperature than that of the ceramic material, as its principal component.
It is noteworthy in the present invention that segregation of the material inclusive of the electrically conductive base material inside the dielectric ceramic layers, that becomes a problem when at least a part of the conductive base metal material is oxidized, or during a process in which a temperature becomes higher than a eutectic point of an oxide of the conductive base metal material and a part of the ceramic material such as when oxidation of the conductive base metal material temporarily occurs in a baking process, does not occur.
Consequently, even when the atmosphere at the time of baking that satisfies the conditions of both ceramic material and conductive base metal material is somewhat adjusted towards the oxidation side in comparison with the prior art condition to invite a temporary oxidizing atmosphere, segregation due to the oxidation of the electrode material does not occur, reduction of the ceramic material can be suppressed, and the drop of performance of the dielectric ceramic layers can be prevented. Segregation of the electrode material occurs inside the dielectric ceramic layers when the conventional electrode materials are used, and the occurrence of the drop of characteristics of the dielectric ceramic layers and its cracks become the problem because the electrode material does not have the original characteristics.
Those metals which can secure electric conductivity even when oxidized can be used as the electrically conductive base metal material constituting the electrode layers described above. In this way, performance of the electrode layers itself can be secured.
Therefore, the present invention can provide a laminate type dielectric device capable of sufficiently exploiting the characteristics of the dielectric ceramic layers by using an economical base metal material for the electrodes.
At least a part of the conductive base metal material may be oxidized according to a second aspect of the invention. In this case, the excellent function and effect described above can be acquired, too.
According to a third aspect of the invention, a bonding layer made of a material that keeps the dielectric characteristics of the dielectric ceramic layer is preferably interposed between one of the dielectric ceramic layers and one of the electrode layers. Here, the material for keeping the dielectric characteristics of the dielectric ceramic layer does not establish insulation between the electrode layer and the ceramic layer, though it does not have the properties equivalent to those of the dielectric ceramic layer. It is of importance that the material does not at all form an insulating layer, but a material that insulates electric conductivity may well be distributed as long as it does not prevent continuity of the electrode/bonding layer/ceramic layer.
According to a fourth aspect of the invention, the bonding layer described above is preferably constituted as the components constituting the dielectric ceramic layer are partially substituted by other atoms. When this condition is satisfied, the bonding layer can be readily formed.
Here, the term xe2x80x9csubstitutionxe2x80x9d represents the case where the material after substitution is classified as the same structure when the atomic arrangement is classified crystallographically.
According to a fifth aspect of the invention, the bonding layer is preferably constituted such that Ca is diffused into the dielectric ceramic layers. In this case, too, the effect of keeping the dielectric characteristics of the dielectric ceramic layers described above can be easily acquired.
According to a sixth aspect of the invention, the conductive base metal material is preferably any one of Cu, Ni, a mixture of Cu and Ni, and/or their alloys. These base metals are economical and have excellent conductivity. Further, their oxides have excellent conductivity. Therefore, these base metal materials can be used for the electrode layers. In any case, the metals satisfying the standard may be used as a mixture.
The mixture or alloy of Cu and Ni can be used because Cu and Ni have a complete solid solution system phase equilibrium.
Because of the complete solid solution system, both mixture and alloy are not melted at a lower temperature than both of Ni and Cu, and can be therefore used. However, limitation of the Ni and Cu composition is necessary.
According to a seventh aspect of the invention, at least one of the dielectric ceramic layers is preferably made of PZT as an oxide mainly having a Pb(Zr, Ti)O3 perovskite structure. This PZT exhibits extremely excellent characteristics as a dielectric and is suitable for the dielectric layer.
According to an eighth aspect of the invention, when at least one of the dielectric ceramic layers is made of PZT, the conductive base metal material is preferably any one of Cu, a mixture of Cu and Ni and their alloys. The dielectric consisting of the Pb(Zr, Ti)O3 as the principal component can be applied limitedly to the metals that are more difficult to oxidize than PbO that remains due to variance of the composition or is added for low temperature baking. At this time, Ni is not suitable because it is more oxidizable than Pb. When Ni is used as a mixture, a Ni oxide may partially be formed. However, the formation of the oxide is not remarkable due to the formation of the Nixe2x80x94Cu alloy, and the reduction of PbO can be mitigated, too.
Next, a ninth aspect of the invention provides a method of producing a laminate type dielectric device formed by alternately laminating dielectric ceramic layers and electrode layers, comprising at least a first step of forming a green sheet by shaping a ceramic material into a sheet form; a second step of applying an electrode paste material to at least one of the surfaces of the green sheet; a third step of laminating the green sheets applied with the electrode paste material, and bonding them together; a fourth step of degreasing a laminate product so bonded; and a fifth step of integrally baking the materials in the electrode layer and the materials in the dielectric ceramic layer within the same process step; wherein a laminate product containing, in the electrode layer as its principal component, an electrically conductive base metal material having greater standard Gibbs free energy for the formation of a metal oxide at a baking temperature than that of the ceramic material, and further containing, at least in the electrode layer, a melting restrictive material for restricting melting of an oxide of the electrically conductive base metal material existing, or formed, in the fifth step, is prepared immediately before the fifth step.
Fusion to the ceramic layer may occur in the fifth step. Since the fifth step is directed to sintering of the ceramic material and the electrode material, the temperature becomes high. In this case, in order to prevent in advance a part of the ceramic material and an oxide of a part of the electrode material from melting due to the eutectic reaction, for example, the melting restrictive material may well be contained in advance in the electrode layer.
This effect can be naturally obtained when a part of the oxide of the electrode material is formed in this case before and during the fifth step.
Next, a tenth aspect of the invention provides a method of producing a laminate type dielectric device formed by alternately laminating dielectric ceramic layers and electrode layers, comprising at least a first step of forming a green sheet by shaping a ceramic material into a sheet form; a second step of applying an electrode paste material to at least one of the surfaces of the green sheet; a third step of laminating the green sheets applied with the electrode paste material, and bonding them together; a fourth step of degreasing a laminate product so bonded; and a fifth step of integrally baking the materials in the electrode layer and the materials in the dielectric ceramic layer within the same process step; wherein a laminate product containing, in the electrode layer as its principal component, an electrically conductive base metal material having a greater standard Gibbs free energy for the formation of a metal oxide at a baking temperature than that of the ceramic material, and further containing, at least in the electrode layer, either one of a melting point raising material for raising the melting point of an oxide of the electrically conductive base metal material formed in the fifth step or a compound between the oxide and the ceramic material and a melting point raising material for raising the melting point of the oxide of the electrically conductive base metal material and a material mixed in the ceramic material, is prepared immediately before the fifth step.
This production method, too, prevents melting of the electrode material in the fifth step in which the temperature becomes high, in the same way as in the ninth aspect of the invention. The difference of this invention from the ninth aspect of the invention resides in means for preventing melting in the baking step by raising the melting point of the material to be melted. Quite naturally, the materials to be melted are diversified such as in the case of the electrode material, the case of the eutectic material of the electrode material and the ceramic material, the case of the eutectic between the material added for a low temperature baking to the ceramic material and the electrode material, the case of the structural material of the laminate product, and so forth.
An eleventh aspect of the invention provides a method of producing a laminate type dielectric device formed by alternately laminating dielectric ceramic layers and electrode layers, comprising at least a first step of forming a green sheet by shaping a ceramic material into a sheet form; a second step of applying an electrode paste material to at least one of the surfaces of the green sheet; a third step of laminating the green sheets applied with the electrode paste material, and bonding them together; a fourth step of degreasing a laminate product so bonded; and a fifth step of integrally baking the materials in the electrode layer and the materials in the dielectric ceramic layer within the same process step; wherein a laminate product containing, in the electrode layer as its principal component, an electrically conductive base metal material having a greater standard Gibbs free energy for the formation of a metal oxide at a baking temperature than that of the ceramic material, and further containing, at least in the electrode layer, either one of a melting point raising material for raising the melting point of an oxide of the electrically conductive base metal material formed in the fifth step or a compound between the oxide and the ceramic material, and a melting point raising material for raising the melting point of the oxide of the electrically conductive base metal material and a material mixed in the ceramic material, and a diffusion restrictive material for restricting diffusion of the oxide of the electrically conductive base metal material into the green sheet as the component elements of the diffusion restrictive material diffuse by themselves into the green sheet in the fifth step, is prepared immediately before the fifth step.
This production method prevents melting of the electrode material by the melting point raising material and improves bonding between the ceramic layer and the electrode layer by the diffusion restrictive material without promoting diffusion of the electrode material, in the same way as the function and effect of the tenth aspect of the invention.
Next, a twelfth aspect of the invention provides a method of producing a laminate type dielectric device formed by alternately laminating dielectric ceramic layers and electrode layers, comprising the steps of: forming a green sheet by shaping a ceramic material into a sheet form; applying an electrode paste material to at least one of the surfaces of the green sheet, the electrode paste material containing as its principal component an oxide of an electrically conductive base metal material having a greater standard Gibbs free energy for the formation of a metal oxide at a baking temperature than that of the ceramic material, and further containing a melting restrictive material for restricting an oxide of the electrically conductive base metal material formed during integral baking from fusing to the green sheet; laminating the green sheets applied with the electrode paste material; and integrally baking the resulting laminate.
The production method of this invention uses a specific electrode paste material as described above. Therefore, it is possible to easily produce the laminate type dielectric device having the electrode layer that contains the electrically conductive base metal material. The resulting laminate type dielectric device can keep excellent characteristics because segregation and diffusion to the ceramic layer due to oxidation of the electrode material are suppressed.
Because the specific electrode paste material is used, expansion of the substance inside the electrode paste material can be suppressed even when large amounts of oxygen (such as air) are charged in the degreasing step before baking, and degreasing can be carried out without any problem.
A thirteenth aspect of the invention provides a method of producing a laminate type dielectric device formed by alternately laminating dielectric ceramic layers and electrode layers, comprising the steps of forming a green sheet by shaping a ceramic material into a sheet form; applying an electrode paste material to at least one of the surfaces of the green sheet, the electrode paste material containing as its principal component an oxide of an electrically conductive base metal material having a greater standard Gibbs free energy for the formation of a metal oxide at a baking temperature than that of the ceramic material, and further containing either one of a melting point raising material for raising the melting point of an oxide of said electrically conductive base metal material formed during integral baking or a compound between said oxide and said ceramic material, and a melting point raising material for raising the melting points of the oxide of the electrically conductive base metal material and materials mixed in the ceramic material; laminating the green sheets applied with the electrode paste material; and integrally baking the resulting laminate.
The production method of this invention, too, uses a specific electrode paste material as described above. Therefore, it is possible to easily produce the laminate type dielectric device having the electrode layer that contains the electrically conductive base metal material. The resulting laminate type dielectric device can keep excellent characteristics because segregation and diffusion to the ceramic layer due to oxidation of the electrode material are suppressed.
Because the specific electrode paste material is used, expansion of the substance inside the electrode paste material can be suppressed even when a large amount of oxygen (such as air) is charged in the degreasing step before baking, and degreasing can be carried out without any problem.
A fourteenth aspect of the invention provides a method of producing a laminate type dielectric device formed by alternately laminating dielectric ceramic layers and electrode layers, comprising the steps of: forming a green sheet by shaping a ceramic material into a sheet form; applying an electrode paste material to at least one of the surfaces of the green sheet, the electrode paste material containing as its principal component an oxide of an electrically conductive base metal material having a greater standard Gibbs free energy for the formation of a metal oxide at a baking temperature than that of the ceramic material, and further containing at least a melting point raising material for raising the melting point of an oxide of the electrically conductive base metal material formed during integral baking or the melting point of a compound between the oxide and the ceramic material, or the melting point of the oxide of the electrically conductive base metal material and materials mixed in the ceramic material, and a diffusion restrictive material for restricting diffusion of the oxide of the electrically conductive base metal material into the green sheet as the component elements of the diffusion restrictive material diffuse by themselves into the green sheet during integral baking; laminating the green sheets applied with the electrode paste material; and integrally baking the resulting laminate.
The production method of this invention, too, uses a specific electrode paste material as described above. Therefore, it is possible to easily produce the laminate type dielectric device having the electrode layer that contains the electrically conductive base metal material. The resulting laminate type dielectric device can keep excellent characteristics because segregation and diffusion to the ceramic layer due to oxidation of the electrode material are suppressed.
Because the specific electrode paste material is used, expansion of the substance inside the electrode paste material can be suppressed even when large amount of oxygen (such as air) is charged in the degreasing step before baking, and degreasing can be carried out without any problem.
In this production method of the laminate type dielectric device, too, the electrically conductive base metal material is preferably any one of Cu, Ni, a mixture of Cu and Ni and their alloy in the same way as in a fifteenth aspect of the invention.
The dielectric ceramic layer preferably comprises PZT as an oxide mainly having a Pb(Zr, Ti)O3 type perovskite structure in the same way as in a sixteenth aspect of the invention. As described already, this PZT exhibits extremely excellent characteristics as a dielectric and is suitable for the dielectric ceramic layer.
The electrically conductive base metal material is preferably Cu, a mixture of Cu and Ni or their alloy according to a seventeenth aspect of the invention.
In such a case, the laminate type dielectric device can be easily produced at a lower cost of production.
The melting restrictive material is preferably a Ca compound in the same way as in an eighteenth aspect of the invention.
The Ca compound is preferably CaCO3 or CaO in the same way as in a nineteenth aspect of the invention. When CaCO3 is employed, CaO is formed during integral baking, and can reliably prevent or restrict melting of the mixture of the ceramic material and the electrically conductive base metal material.
According to a twentieth aspect of the invention, when the amount of the electrode layer exclusive of the CaCO3 or CaO is 100 wt %, CaCO3 or CaO is preferably contained within a range of 1 wt % to 15 wt % calculated as CaO. When the amount is not more than 1 wt %, the segregation restriction effect of the component element Cu is not sufficient, and when it exceeds 15 wt %, on the other hand, the specific resistance increases by one order of magnitude and deterioration of conductivity is observed.
According to a twenty-first aspect of the invention, the melting point raising material is preferably a material which exhibits a change of a melting point of a complete solid solution system when it is reacted with a reaction material between the ceramic material and an oxide of the electrically conductive material, or with a reaction material between the oxide of the electrically conductive base metal material and a material mixed in the ceramic material or with a reaction material made of an oxide of the electrically conductive base metal material, and has a higher melting point than that of the reaction materials, or a material which exhibits a change of a eutectic type melting point when it is reacted with any one of the reaction materials, in which the eutectic point with the reaction material exists within a range of an amount exceeding 0 wt % to 5 wt % calculated as the amount of the oxide of the component element of the reaction material, and which has a higher melting point than that of the reaction material.
The term xe2x80x9cchange of melting point of complete solid solution systemxe2x80x9d means that a melting point (reaction temperature) of a mixture (alloy) exists within the temperature zone interposed by the melting points (reaction temperatures) of two individual substances (Ni and Cu in FIG. 31, for example). Quite naturally, it is necessary at this time to add a material having a higher melting point so as to raise the melting point. In the case described above, the material must have a higher melting point than that of the reaction inducing material as any one of the compound or mixture of the ceramic material and the oxide of the electrically conductive base metal material, the oxide of the conductive base metal material and the substance mixed in the ceramic material and the oxide of the conductive base metal material. Incidentally, the term xe2x80x9cmixturexe2x80x9d may include those which can either partially or wholly create melting by the eutectic reaction, etc, and need not necessarily be limited to the materials that are merely mixed.
The change of the melting point of the complete solid solution system need not necessarily occur in the whole composition zone (0 to 100%) but may well occur in the region of a necessary addition amount.
Next, the content of the materials which exhibit the change of the eutectic point and whose eutectic point exists within the range of 0 to 5 wt % when calculated as the oxide of the constituent element, and their function and effect, will be explained.
Such a material has a phase equilibrium diagram shown in FIG. 32, for example. The drawing represents a phase equilibrium diagram of Ag and Bi by way of example. However, this is merely illustrative and has nothing to do at all with the actual additives and the reaction materials.
Ag and Bi have the eutectic point at Ag 2.5% and Bi 97.5%. As represented by the phase equilibrium diagram of FIG. 32, the eutectic material is ideally formed with the Ag amount within a broad range of 0.3 to 98%. In the case of powder, however, there is the region in which the formation of the eutectic material is retarded due to the specific surface area, the degree of mixing, non-uniformity, etc, that is, the composition range in which the melting temperature shifts toward a higher temperature side. This composition range is one that is far from the eutectic point.
When the eutectic point deviates either to the left or to the right in the phase equilibrium diagram, that is, when the eutectic point exists in a range where the amount of one of the material is small, the temperature at which eutectic occurs does not have a great difference from the melting point (reaction temperature) of the material of the greater amount.
For the two reasons described above, even when a material generating the phase equilibrium of the eutectic system is added, it becomes the melting point raising material in a region somewhat deviated from the eutectic point if the eutectic point exists in the region of the material having a smaller amount, and the composition zone at this time is a suitable amount as the addition amount to the electrode material. Here, the term xe2x80x9csuitable amount for the electrode materialxe2x80x9d means the amount that can suppress the drop of conductivity of the electrode.
To raise the melting point, the melting point of the material described above must be higher than that of the reaction material.
According to a twenty-second aspect of the invention, the melting point raising material is preferably a material that exhibits a change of a melting point of a complete solid solution system when it is reacted with a reaction material comprising a mixture of the ceramic material and an oxide of the electrically conductive material at a temperature not higher than 680xc2x0 C., or with a reaction material as a mixture of the oxide of the of the electrically conductive base metal material and a material mixed in the ceramic material or with a reaction material made of an oxide of the electrically conductive base metal material, and that has a higher melting point than that of the reaction materials, or a material which exhibits a change of an eutectic type melting point when it is reacted with any one of the reaction materials, in which the eutectic point with the reaction material exists within a range of an amount exceeding 0 wt % to 5 wt % calculated as the amount of the oxide of the component element of the reaction material, and which changes to, or generates, any of materials having a higher melting point than that of the reaction materials.
In this case, it is sufficient if the construction of the twenty-first aspect of invention can be achieved at 680xc2x0 C. or below.
The eutectic phenomenon between PbO and Cu2O, that might be one of the factors of melting of the electrode material, occurs at 680xc2x0 C. If oxidation of the electrode material is not complete, Cu and Cu2O generate the eutectic reaction. Therefore, since the eutectic reaction may occur at 680xc2x0 C. or below, melting can be suppressed if the melting point raising material is formed before the eutectic reaction takes place. The material (material in the starting materials) need not be limited to the inorganic materials.
The melting point raising material is preferably a Mg compound or a Sr compound according to a twenty-third aspect of the invention.
The Mg compound is preferably MgO and the Sr compound is preferably SrCO3 according to a twenty-fourth aspect of the invention. When MgO or SrCO3 is employed, it can reliably raise the melting point of at least one kind of the compound or mixture of the ceramic material and the electrically conductive base metal material, the mixture of the oxide of the conductive base metal material and the materials mixed in the ceramic material, and the oxide of the conductive base metal material. The additives are not particularly limited to those described above so long as they fall in the range of this concept.
In all the cases described above, the Ca compound, the Mg compound and Sr compound may be oxides or carbonates. The oxide need not be limited to CaO, and materials outside the range of Ca:O=1:1 may be used if such exist. This also holds true of the Mg oxide and the Sr oxide.
The following steps (1) to (3) are available, for example, when the laminate product is produced from the paste material:
(1) evaporation of solvent and binder in air
(2) metallizing of electrode portion
(3) baking of ceramic portion
The reason why CuO, for example, is used as the principal component in the present invention is because the production process includes (1) evaporation of a solvent and a binder in air. CuO changes to Cu or Cu2O during the steps (2) and (3). In the paste material containing Cu, Cu changes (ix oxidized) to CuO or Cu2O in the step (1), and expansion resulting from oxidation in turn results in the occurrence of de-lamination. Therefore, the Cu paste material may well be degreased in a N2 atmosphere, for example, and is then baked.
However, degreasing can also be conducted in air when Cu is mixed besides CuO, such as when Cu+CuO is used as the principal component. Therefore, the principal components need not be limited to CuO alone.
According to a twenty-fifth aspect of the invention, when the amount of the electrode layer exclusive of the MgO or the electrode layer exclusive of MgO and the diffusion restrictive material is 100 wt %, MgO is contained preferably in an amount within the range of 0.2 to 20 wt %. When the amount is less than 0.2 wt %, diffusion of the component element Cu occurs, and segregation possibly occurs, too. When it exceeds 20 wt %, on the other hand, the specific resistance drastically increases, and the problem occurs in conductivity of the electrode.
According to a twenty-sixth aspect of the invention, when the amount of the electrode layer exclusive of SrCO3 or the electrode layer exclusive of SrCO3 and the diffusion restrictive material is 100 wt %, SrCO3 is contained preferably in an amount within the range of 10 to 15 wt % calculated as SrO. The melting point raising effect cannot be expected when the content is less than 10 wt %.
According to a twenty-seventh aspect of the invention, the diffusion restrictive material is preferably a Ca compound.
According to a twenty-eighth aspect of the invention, the Ca compound described above is particularly preferably CaCO3 or CaO. while this CaO restricts melting, diffusion and segregation of the mixture of the ceramic material and the electrically conductive base metal material, the constituent element Ca diffuses into the dielectric ceramic layer, so that the bonding strength between the electrode layer and the dielectric ceramic layer can be improved.
According to a twenty-ninth aspect of the invention, when the amount of the electrode layer exclusive of CaCO3 or CaO and the melting point raising material is 100 wt %, CaCO3 or CaO is contained preferably within a range of an amount exceeding 1 wt % to 15 wt % calculated as CaO. When the amount is not more than 1 wt %, the segregation restrictive effect of the component element Cu is not sufficient and when it exceeds 15 wt %, on the other hand, the specific resistance increases by one digit and deterioration of conductivity is observed.
Particularly when the diffusion restrictive material is the Ca compound, further preferably CaCO3 or CaO and the melting point raising material is the Mg compound or the Sr compound, further preferably MgO or SrCO3, segregation and diffusion of the conductive base metal material can be suppressed, and the bonding strength can be improved.
According to a thirtieth aspect of the invention, it is preferred that a designated electrode paste material is applied to both surface of the green sheets, and the green sheets applied with the electrode paste material are laminated while sandwiching electrically conductive powder or thin film, and are then integrally baked.
As described above, when the green sheets are laminated while interposing powder or the thin film having conductivity and are integrally baked, the electrode layer can more reliably secure electric conductivity. For example, portions having low conductivity have been formed in the past due to non-uniformity of the paste material printed, but this invention can acquire the laminate type dielectric device having high conductivity as a whole.
Next, a thirty-first aspect of the invention provides a laminate type dielectric device formed by alternately laminating dielectric ceramic layers and electrode layers, wherein the electrode layers are made of an electrically conductive base metal material having a greater standard Gibbs free energy for the formation of a metal oxide at a baking temperature than that of a ceramic material constituting mainly the dielectric ceramic layers, and wherein, when a reference straight line orthogonally crossing any one of the dielectric ceramic layers and two electrode layers above and below the dielectric ceramic layer is assumed, a portion containing a Ca amount per unit volume greater than A+B, where A is a Ca amount per unit volume contained at a center point at the center of the dielectric ceramic layer between the two electrode layers in a thickness-wise direction and B is a Ca amount per unit volume contained in either the above or below one of the electrode layers, exists on the reference straight line connecting the electrode layer containing B to the center point.
In the present invention, the constituent element Ca exists concentratedly at the boundary portion between one of the electrode layers and one of the dielectric ceramic layers. The existence of the component element Ca restricts diffusion and segregation of the electrode material into the dielectric ceramic layer, or improves the bonding strength between the electrode layer and the dielectric ceramic layer.
Due to restriction of diffusion and segregation of the electrode material into the dielectric ceramic layers, it is possible to obtain dielectric ceramic layers having excellent performance.
It should be particularly noted hereby that the present invention can be distinguished from the case where the component element Ca is in advance contained in the dielectric ceramic layers, from the distribution of the component element Ca in the product.
The effect described above cannot be obtained when the material to which the component element Ca is added in advance to the dielectric ceramic layers, such as (Pb, Ca) (Zr, Ti)O3 is used, and Ca is uniformly distributed in this case.
Next, a thirty-second aspect of the invention provides a laminate type dielectric device formed by alternately laminating dielectric ceramic layers and electrode layers, wherein the electrode layers are made of an electrically conductive base metal material having a greater standard Gibbs free energy for the formation of a metal oxide at a baking temperature than that of a ceramic material constituting mainly the dielectric ceramic layers, and at least one of the electrode layers contains Mg as a component element.
In this invention, the component element Mg exists inside the electrode layer, suppresses diffusion and segregation of the electrode material and provides excellent characteristics. At this time, the component element Mg need not exist in all of the electrode layers.
First, even when MgO in such a small amount that cannot be detected by means of EPMA is added to the electrode paste, the existence of such a small amount of Mg exhibits the effect of suppressing diffusion and segregation of the electrode material into the dielectric layers.
Second, the existence of the component element Mg provides a great effect of suppressing diffusion and segregation of the electrode material into the dielectric ceramic layers, and there is the possibility that sufficient performance can be obtained even when diffusion restriction is not promoted in all the electrode layers. For example, even when the suppression effect of diffusion and segregation is not promoted in one electrode layer among ten electrode layers, more excellent overall performance can be obtained than in the prior art devices because the other electrode layers restrict diffusion and segregation.
For the two reasons described above, the component element Mg may be contained in such an amount that it can be detected in only a limited part of an arbitrary electrode layer.
The two reasons described above can be applied not only to the component element Mg but also to other constituent elements added to restrict diffusion and segregation.
Next, a thirty-third aspect of the invention provides a laminate type dielectric device formed by alternately laminating dielectric ceramic layers and electrode layers, wherein the electrode layers are made of an electrically conductive base metal material having a greater standard Gibbs free energy for the formation of a metal oxide at a baking temperature than that of a ceramic material constituting mainly the dielectric ceramic layers, and wherein the Mg content per unit volume in the electrode layers is greater than a mean value of the Mg content per unit volume in said dielectric ceramic layers.
This invention is basically the same as the thirty-second aspect of the invention described above, but sets the reference for judging the existence/absence of detection from an error (error in X-ray intensity, for example, in a measuring apparatus (EPMA, for example) of the component elements. However, the thirty-third aspect of the invention is not applied when the ceramic material apparently contains Mg.
Next, a thirty-fourth aspect of the invention provides a laminate type dielectric device formed by alternately laminating dielectric ceramic layers and electrode layers, wherein the electrode layers are made of an electrically conductive base metal material having a greater standard Gibbs free energy for the formation of a metal oxide at a baking temperature than that of a ceramic material constituting mainly the dielectric ceramic layers, and wherein the Sr content per unit volume in the electrode layers is greater than a mean value of the Sr content per unit volume in the dielectric ceramic layers.
When the addition amount of the component element Sr in the electrode layer is small, the intended effect cannot be obtained. Therefore, less than 10 wt % of Sr is contained in the ceramic material. The component element Sr suppresses diffusion and segregation of the electrode material and provides excellent characteristics.
For the same reason as described above, the electrically conductive base metal material is preferably any one of Cu, Nixe2x80x2 a mixture of Cu and Ni and their alloys according to a thirty-fifth aspect of the invention.
According to a thirty-sixth aspect of the invention, the dielectric ceramic layers described above preferably comprise PZT as an oxide mainly having a Pb(Zr, Ti)O3 type perovskite structure.
For the same reason as described above, the electrically conductive base metal material is preferably any one of Cu, Ni, a mixture of Cu and Ni and their alloys according to a thirty-seventh aspect of the invention.
Next, a thirty-eighth aspect of the invention provides an electrode paste material for forming electrode layers in a laminate type dielectric device formed by alternately laminating dielectric ceramic layers and the electrode layers, wherein the electrode paste material comprises CuO as its principal component, and contains a melting restrictive material for restricting melting of a copper oxide to the dielectric ceramic layers during integral baking.
When the electrode paste material according to the present invention is used, expansion due to oxidation can be suppressed during the degreasing step for oxidizing carbon, and a laminate type dielectric device having the Cu-containing electrode layers can be easily produced. The laminate type dielectric device so produced can have excellent characteristics.
In other words, when a laminate product interposing a CuO paste material, not containing an additive, between ceramic materials is integrally baked, oxidation of Cu is observed when the laminate product is produced by increasing an oxygen partial pressure rather than under a reducing condition for restricting reduction of the ceramic material and reducing the Cu electrode material. Since the PZT type material is an oxide, the melting phenomenon due to the eutectic reaction, for example, occurs between the oxides.
When this melting occurs in large quantities at a low temperature, the melted material flows into the ceramic material because baking of the ceramic material has not proceeded. When the dielectric ceramic layer after baking is split and is inspected, the Cu-containing compound is found segregated but not diffused. The segregated material does not always have piezoelectric characteristics like the ceramic material, but not only deteriorates the piezoelectric characteristics but also results in the occurrence of cracking during driving. When the melting temperature is high or the melting amount is small, sintering of the ceramic proceeds with the result that diffusion occurs without reaching segregation. The diffusion material does not always have the piezoelectric characteristics, and the problem occurs in the same way as in the case of segregation.
In the electrode paste material comprising CuO paste material to which the specific material is added, segregation and diffusion of the Cu-containing compound can be suppressed in the ceramic material because melting is restricted.
Next, a thirty-ninth aspect of the invention provides an electrode paste material for forming electrode layers in a laminate type dielectric device formed by alternately laminating dielectric ceramic layers and the electrode layers, wherein the electrode paste material comprises CuO as its principal component, and contains a melting point raising material for raising a melting point (e.g. eutectic point) of the copper oxide or a melting point of a compound between the copper oxide and ceramic material constituting said dielectric ceramic layers, or melting points of materials mixed in the ceramic material and the copper oxide during integral baking.
When the electrode paste material according to the present invention is used, segregation and diffusion of the Cu-containing compound can be suppressed due to restriction of melting resulting from the rise of the melting point.
Next, a fortieth aspect of the invention provides an electrode paste material for forming electrode layers in a laminate type dielectric device formed by alternately laminating dielectric ceramic layers and the electrode layers, wherein the electrode paste material comprises CuO as its principal component, and contains a melting point raising material for raising a melting point of the copper oxide or a melting point of a compound between the copper oxide and ceramic material constituting the dielectric ceramic layers, or melting points of materials mixed in the ceramic material and the copper oxide during integral baking, and a diffusion restrictive material for restricting diffusion of the copper oxide into the dielectric ceramic layers during integral baking, the components of the diffusion restrictive material diffusing by themselves into the dielectric ceramic layers during integral baking.
When the electrode paste material according to the present invention is used, segregation and diffusion of the Cu-containing compound can be suppressed due to the rise of the melting point and restriction of diffusion, and the bonding strength between the electrode layers and the dielectric ceramic layers can be improved.
According to a forty-first aspect of the invention, the at least one of the dielectric ceramic layers described above preferably consists of PZT as an oxide mainly having a Pb(Zr, Ti)O3 type perovskite structure.
In the electrode paste material described above, the melting restrictive material is preferably a Ca compound according to a forty-second aspect of the invention.
For the same reason as described above, the Ca compound is preferably CaCO3 or CaO according to a forty-third aspect of the invention.
For the same reason as described above, when the amount of the electrode layers exclusive of CaCO3 or CaO is 100 wt %, it is preferred that CaCO3 or CaO is contained within a range of an amount exceeding 1 wt % to 15 wt % calculated as CaO according to a forty-fourth aspect of the invention.
In the electrode paste material described above, too, it is preferred that the melting point raising material is either a material that exhibits a change of a melting point of a complete solid solution system when it is reacted with a reaction material between the ceramic material and a copper oxide, or with a reaction material between the copper oxide and a reaction material made of the copper oxide, and has a higher melting point than that of the reaction materials, or a material which exhibits a change of a eutectic type melting point when it is reacted with any one of the reaction materials, in which the eutectic point with the reaction material exists within a range of an amount exceeding 0 wt % to 5 wt % calculated as the amount of the oxide of the component element of the reaction material, and which has a higher melting point than that of the reaction material, according to a forty-fifth aspect of the invention.
According to a forty-sixth aspect of the invention, the melting point raising material is either a material which exhibits a change of a melting point of a complete solid solution system when it is reacted with a reaction material comprising a mixture of the ceramic material and a copper oxide at a temperature lower than 680xc2x0 C., or with a reaction material comprising a mixture of the copper oxide and a material mixed in the ceramic material, or with a reaction material comprising the copper oxide, and has a higher melting point than that of the reaction materials, or a material which exhibits a change of an eutectic type melting point when it is reacted with any one of the reaction materials, in which the eutectic point with said reaction materials exists within a range of an amount exceeding 0 wt % to 5 wt % calculated as the amount of the copper oxide, and which changes to, or generates, a material having a higher melting point than that of the reaction materials.
According to a forty-seventh aspect of the invention, the melting point raising material in the electrode paste material described above is preferably a Mg compound or a Sr compound.
According to a forty-eighth aspect of the invention, in particular, the Mg compound described above is preferably MgO and the Sr compound is preferably SrCO3.
According to a forty-ninth aspect of the invention, when the amount of the electrode paste material exclusive of MgO or the electrode paste material exclusive of MgO and the diffusion restrictive material is 100 wt %, MgO is preferably contained in an amount within the range of 0.2 wt % to 20 wt % calculated as CaO.
According to a fiftieth aspect of the invention, when the amount of the electrode paste material exclusive of SrCO3 or the electrode paste material exclusive of SrCO3 and the diffusion restrictive material is 100 wt %, SrCO3 is preferably contained in an amount within the range of 10 wt % to 15 wt % calculated as SrO.
According to a fifty-first aspect of the invention, the diffusion restrictive material in the electrode paste material is preferably a Ca compound.
For the same reason as described above and according to a fifty-second aspect of the invention, the Ca compound is particularly preferably CaCO3 or CaO.
According to a fifty-third aspect of the invention, when the amount of the electrode paste material exclusive of CaCO3 or CaO and the melting point raising material is 100 wt %, CaCO3 or CaO is preferably contained within a range of an amount exceeding 1 wt % to 15 wt % calculated as CaO for the same reason as described above.
According to fifty-fourth and fifty-eighth aspects of the invention, the electrode paste material preferably contains a cooperative material comprising at least one kind of the principal components constituting the dielectric ceramic layers. In this case, the bonding condition between the resulting electrode layers and the dielectric ceramic layers can be improved.
According to fifty-fifth and fifty-ninth aspects of the invention, the electrode paste material further preferably contains a cooperative material made of substantially the same material that constitutes the dielectric ceramic layers. In this case, the bonding condition between the resulting electrode layers and the dielectric ceramic layers can be further improved.
According to fifty-sixth and sixtieth aspects of the invention, the amount of the cooperative material is preferably less than 25 wt %. When the amount exceeds 25 wt %, the electrode becomes discontinuous, and upper and lower ceramic layers adhere to each other. As a result, conductivity drops and the drop of performance occur. Therefore, the amount of the cooperative material is more preferably 15 wt % or below according to fifty-seventh and sixty-first aspects of the inventions.
A greater standard Gibbs free energy for the formation of a metal oxide of the material means that the material is xe2x80x9cmore difficultly oxidizablexe2x80x9d. For example, Gibbs free energy for the formation of a Cu oxide at 1,000xc2x0 C. is about xe2x88x9240. It is bout xe2x88x9215 for a Pb oxide and about xe2x88x9260 for a Ni oxide. Therefore, Cu, Pb and Ni are less oxidizable in this order (see FIG. 36).
As shown in FIG. 31, Cu and Ni assume the complete solid solution system phase equilibrium. Therefore, a great change of the crystalline system does not occur, and the property changes linearly in accordance with the change of the composition. Therefore, linear calculation is conducted in accordance with the Gibbs free energy composition, and the mixture or alloy is employed within the range in which it is not smaller than Gibbs free energy for oxidizing Pb.
In the case of a mixture or alloy of [90%Cu+10%Ni], for example, the calculation result becomes (xe2x88x9240)xc3x970.9+(xe2x88x9260)xc3x9701=xe2x88x9242. Since this value is greater than the Gibbs free energy (xe2x88x9245) for oxidizing Pb, the mixture or alloy can be used.
Whether or not the composition typified above can be used is decided from the read value of the calculation at 1,000xc2x0 C. Therefore, this is a method of limiting the composition when the baking temperature is mainly 1,000xc2x0 C. When the baking temperature is different from the example given above, the read numeric value is changed to the value at the baking temperature (see FIG. 36), and the calculation is similarly conducted. In this way, the usable composition can be selected.
In the case of non-Pb ceramic material, the element that is least oxidizable is used in place of Pb in the starting material to limit the Cuxe2x80x94Ni composition. In the case of the ceramic material using only those materials which are more easily oxidizable than Ni as the starting material, limitation of the Cuxe2x80x94Ni does not exist, and Ni can be applied, too.